In a typical cellular wireless communication system (wireless telecommunications network), an area is divided geographically into a number of cell sites, each defined by a radio frequency (RF) radiation pattern from a respective base station. The base stations of the cells are then coupled to a switch or gateway (hereafter “switching system”) that provides connectivity with a transport network and/or to a signaling network. When a wireless client station, such as a cellular telephone, personal digital assistant, pager, or appropriately equipped portable computer, for instance, is positioned in a cell, the client station may then communicate via an RF air interface with the base station of the cell. Consequently, a communication path can be established between the client station and the network, via the air interface, the base station and the switching system.
As a general matter, each base station (or, more generally, cell site) in the system will typically include a number of channel element cards that pass communications between the air interface and the switching system. Each channel element card may support transmission of communications on a number of air interface communication channels (e.g., air interface channels, whether traffic channels or control channels) at once. In turn, a wireline trunk (e.g., a T1 line) or other link will typically couple a group of channel element cards with the switching system, transporting multiple communications at once between the cell site and the switching system.
The switching system will then typically function to control operation of the various base transceiver stations e.g., (i) controlling handoff as mobile client stations move between base stations, and (ii) controlling allocation of air interface resources. Additionally, the switching system may function as a transcoder, to convert the protocol of communications being passed between the air interface and downstream network elements. For instance, in a Code Division Multiple Access (CDMA) network, the air interface may carry voice signals as Enhanced Variable Rate Codec (EVRC) encoded data, while the transport network may carry voice signals as Pulse Code Modulation (PCM) encoded data. In such a network, the switching system may include a mechanism to convert between EVRC and PCM, so as to allow voice communications to pass seamlessly between the air interface and the transport network. Other examples are possible as well.
Generally speaking, the switching system may include a number of handler modules that will function to handle cell site communications, such as to perform the protocol conversion function noted above for instance. The handler cards may then be coupled to a switching processor, which functions to route communications between the handler cards and the transport network and/or signaling network.
In operation, communications may thus pass from client stations over the air interface and through cell site channel element cards, over a T1 line to the switching system. At the switching system, the communications may then pass through handler cards to the switching processor, which may then route the communications onto a transport or signaling network. Similarly, communications may pass from a network to the switching processor and in turn through protocol handler cards and over a T1 line to a cell site. At the cell site, channel element cards may then pass the communications along to the air interface, for transmission to client stations.